This invention relates generally to invasive medical radiotherapy and, more particularly, to a radiation source for use in invasive medical treatment, and to a method for making it.
Physicians now use radiation to treat an increasing number of medical problems. One form of radiation treatment involves the insertion of a radiation source into a patient's body to irradiate a limited area of the body for a controlled period of time. Typically, a surgeon inserts a longitudinal radiation source into the patient's body through a lumen of an implanted guide catheter. This procedure often requires a radiation source to exhibit both high flexibility and an effectively high level of radioactivity, particularly for cardiovascular radiotherapy. Furthermore, the radiation source must provide consistent levels of radiation over its entire length.
During implantation, the radiation source might be required to travel through tortuous pathways within a patient's body, such as the coronary arteries. Furthermore, the area requiring treatment might be characterized by tortuous twists and bends. A radiation source must therefore be sufficiently flexible to navigate such pathways without injuring the patient or damaging itself.
Once the radiation source has been inserted into the patient's body, the total dosage of radiation will be determined by the level of radioactivity of the radiation source, and by the length of time the targeted tissue is exposed to the radiation source. Radiation sources having higher radiation levels provide for shorter exposure times, which lowers both the time duration of a procedure and the level of risk involved in the procedure. This risk is particularly important in situations where the guide catheter causes significant obstruction to the profusion of the blood. However, existing technologies provide for higher levels of radioactivity at the expense of flexibility, thus placing an upper limit on the radiation levels available for treating tortuous pathways.
A limiting factor on the design of such radiation sources is the risk of overexposing a patient to radiation due to inconsistent levels of radiation along the length of the radiation source. The radiation source is brought into close proximity with portions of the patient's body, and a particularly "hot" portion of the radiation source can therefore overexpose an adjacent portion of the patient's body. Likewise, longitudinal sections having a lower than desired radiation level can provide lower than desired levels of radiation treatment. Thus, the radiation level along a radiation source must be kept as longitudinally consistent as possible. It is known that longitudinal uniformity is important, and that a preferred level of uniformity is a maximum 10% variation.
It is known, for example, that a radiation source can be formed in a cavity within a wire or within a tube (also known as a ribbon), and can include a plurality of rigid pellets, made from a radioactive isotope, that are embedded at intervals along the wire with spacers positioned between the pellets. The spacers function to give this source wire some flexibility despite the presence of the rigid pellets. The flexibility is restricted, however, to the areas between the pellets. Furthermore, the pellets form a series of nonuniform radiation hot spots, causing tissue around the source wire to be irradiated unevenly. Longer spacers improve the source wire's flexibility, however they cause the distribution of radiation to be less uniform and less continuous, and thus a trade off must be made between flexibility and radiation uniformity.
It has been suggested that an isotope could be carried in a liquid, and passed into, and then out of a passage in a catheter. However, when the catheter assumes a strongly bent position, such as in a tortuous passage, a portion of the passage could change in cross-sectional shape, and the quantity of the isotope that could be located in that portion would vary. Thus, the catheter would have local radiation levels that vary with the bent shape of the catheter, and would not maintain a uniform radiation level distribution.
Accordingly, there has existed a definite need for an invasive medical treatment radiation source, where the radiation source exhibits high flexibility and high levels of radioactivity, the radioactivity being distributed in a uniform and continuous fashion throughout the radiation source. The present invention satisfies these and other needs, and provides further related advantages.